Conventional aircraft collision avoidance systems are cooperative in nature. Each aircraft includes a transponder that transmits a detectable signal providing identification and positioning information to other aircraft and ground based systems. Aircraft and ground based systems receive this transmitted data for all aircraft in a defined area and generate a three-dimensional map indicating the aircraft positions.
Most aircraft also include a radar system. Radar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. A radar system has a transmitter that emits either radio waves or microwaves that are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar is used in addition to monitoring transponder signals. Radar is effective in all weather conditions, but requires significant effort to focus. As such, radar is useful for determining range and bearing, but is not particularly useful for determining precise size and definition.